User manual

Note: The reference system is used for displaying coordinates but also for entering

coordinates in any Aladin forms.

Pixel value

The pixel value can be given in three ways:

 8 bits: The “one colour” level (usually grey) is used for current display. It gives a value

between 0 and 255 that depends mainly on the contrast parameters that were

chosen. If the image is in JPEG, only this display mode will be available;

 Raw file: The value used for coding pixels in the image file;

 Full: The “physical” value for the pixel. This value is given from the code value (raw)

multiplied by a scaling factor supplied with the image (BSCALE – according to the

FITS format) and is offset from the origin (BZERO). This last value (Full) is the most

significant and is the one given by default (Full=raw*BSCALE+BZERO). If the

BSCALE and BZERO parameters and not given, the “Full” value for a given pixel will

be the same as its “Raw” value.

Saving the current information

Values in the information band are continuously modified following the movements of

the mouse. However, a click with the mouse in the view will save the current values

(location + pixel) and these values will appear for a short moment in magenta. These

values will be saved in the “Location” and “Pixel” fields and will be displayed again by

entering the corresponding field with the mouse. Doing so, they can be pasted in the

clipboard in order to be paste in another application.

Giving the location, the name of an object

Menu: Tool => Object name resolver …

Short key: Ctrl+R

It is possible to give a location directly in the “Location” field. The referential used should

then correspond to the one specified (J2000, B1950d, XYimage…). When validating

with Enter the location that was typed, the Reticle (magenta cross) will move to the

corresponding location in the view, and the view will be centred on this location. This

location can eventually be off the image.

It is also possible to type astronomical object identification. In this case, the validation

key (Enter) will lead first to an automatic query of the “CDS Sesame” service, which will

give back the best known location for the object by looking into the SIMBAD or NED

data base and some large astronomical catalogues in Vizier. Then, using the coordinates

obtained, Aladin will move the Reticle and centre the view on the location. This function

is also accessible via the menu “Tool => Object name resolver”.

Tip: If the view is still empty, typing a location or an astronomical object identification

will create three planes by automatic query of the DSS image server (the CDS one by

default), of SIMBAD and of NED.